APU fuel drain mast

[AeroTech]

Hi,

I posted the following questions on Tech Log. So far I didn't receive any answer. I hope Engineers & Technicians of this forum will answer my questions.


"There are two drain masts. The one just aft of the port wheel-well is shared with the hydraulic reservoir vent and is a shrouded line enclosing the APU fuel supply line, this collects any leakage of fuel into the shroud which can be drained when a stop cork is pushed up in the wheel-well. If fuel drains when the stop cork is pushed, it indicates a leak in the APU fuel line".

This is an excerpt from this link: The 737 APU


a) I am wondering if this excerpt is valid for the B737 NG, the classic, or both? or not valid at all for any B 737 ?

b) If the B737 NG is fitted with the "stop cork" (mentioned in the excerpt), where the leakage of the fuel goes in flight if there is a leak in the APU fuel line?

c) Are other aircraft (Boeing, Airbus, Bombardier, Embraer,...) fitted with APU fuel drain mast ? Is it similar to the B737 ?

Feedback appreciated.

Regards

[allosaurus]

its "stop cock" not "cork".I think spell checker thought this was a rude word.

[HMV]

Have a look here [url=http://www.sjap.nl/]Sjap's 737 maintenance exchange

They are the specialists on the 737...

Good luck

Gerrit

[grounded27]

I can speak for the DC-10/MD-11, the shroud if checked regularly can contain an amount of fuel that can sometimes be measured as acceptable. Excessive leakage will empty in flight or on the ground out of the drain mast. I would immagine other designs to be the same or similar.

[tech-line]

It's valid for NG, from memory on NG nil leak allowed. The drain mast is also the hyd overfill/ vent system
I have seen people hit whilst walking under APU with skydrol.
You also use drain mast(fuel part) to check fcu for leaks. 18 psi must hold for 'X' amount of hrs allowed to drop a few psi.
Been a while since I have done heavy maintenance.
Hope that helps.

[KBPsen]

c) Are other aircraft (Boeing, Airbus, Bombardier, Embraer,...) fitted with APU fuel drain mast ? Is it similar to the B737 ?Any aircraft with the APU in the tail are, by necessity, the same. Otherwise you would have a fuel line in the same space as passengers and/or crew. With a shroud you have effectively removed the fuel line from that space, but then need means of removing/checking any leaked fluids.

[aeromech3]

Fuel lines which run through the pressurized areas are typically shrouded, as is the case for supply to the rear mounted APU's. The shroud seals the fuel line from the 'cabin' pressurized areas should there be a fuel leak; it will have a drain point at its lowest point, in most cases this is an open mast but there might be a plunger type drain valve which would need to be pushed up to check for fuel presence during say a pre-flight; fuel is unacceptable in most cases but there could be a collection of condensate and therefore it would be wise to catch the liquid, so as not to be mistaken. In some types with auxiliary rear fuel tanks, this same drain point might be connected to the fuel cell cavity drains. The shroud would be checked for integrity during heavy maint, usually with a low pressure check rig, as nowadays ground pressurization checks are not encouraged. Liquid from upper drain masts would normally indicate a component leakage.

[awad]

any of you guys have heard about apu and trim tank shroud line on a380..
why the apu shroud line is smaller than the trim tank shroud?

[Dougie_diesel]

@tech-line,
I've never seen a stopcock on the NG, and in 10 years I've never had any test or function of one? Can you elaborate? Location/description?

Also, the fuel line is only shrouded from the APU compartment bulkhead FWD, so the drain you are talking about pressure testing has no way of containing fuel from defective FCU.

Thirdly, the drain shared by the HYD overflow is just aft of the LH main wheel well, so it would have to be an explosive overflow, an a really short 737 variant to cover someone walking under the APU. I've only ever seen it expel skydrol once, when someone forgot to pull breakers during a LG manual extension test, and it wasn't that spectacular.

To the OP,
With a great deal of experience, I can say this is not valid for the NG, unless it is an option all the operators I have worked for have declined